/Engine/Plugins/MovieScene/MovieRenderPipeline/Source/MovieRenderPipelineCore/Public/MovieRenderPipelineDataTypes.h
What is the current overall state of the Pipeline? States are processed in order from first to last and all states will be hit (though there is no guarantee the state will not be transitioned away from on the same frame it entered it). Used to help track overall progress and validate code flow.
enum EMovieRenderPipelineState { Uninitialized = 0, ProducingFrames = 1, Finalize = 2, Export = 3, Finished = 4, }